a) Field of the Invention
This invention relates to a tired roller for finishing a paved surface of asphalt or the like by performing rolling compaction of the paved surface with rubber tires in the form of wheels.
b) Description of the Related Art
A tired roller is a construction vehicle, which is equipped with rubber tires and is adapted to rolling-compact a paved surface of asphalt by the rubber tires. When applying asphalt paving, a roadbed which has not been paved with asphalt is first roughly finished by performing rolling compaction with a construction vehicle having steel wheels and then, a paved surface of asphalt is formed on the roadbed. The tired roller performs rolling compaction of the paved surface with the rubber tires to finish the paved surface. The present invention is to make improvements in a travelling mechanism of such a tired roller. To facilitate the understanding of the present invention, fundamental technical details of a conventional general tired roller will first be described with reference to FIG. 9 and FIG. 10. FIG. 9 is a side view showing the overall image of the conventional general tired roller by cutting off a rear section, and FIG. 10 is a rear view of a left half of the tired roller.
Illustrated in FIG. 9 and FIG. 10 are a tired roller main body 1 as a self-traveling vehicle body capable of travelling by itself with rubber tires, a prime mover 2 as a power source for the tired roller main body 1, a hydraulic pump 3 for an HST, said hydraulic pump being driven by said prime mover 2, a hydraulic motor 4 for the HST, said hydraulic motor being adapted as a traveling motor driven by pressure oil from said hydraulic pump 3, a speed reduction gear 5 connected to an output shaft of the hydraulic motor 4 and adapted as a speed reduction mechanism for reducing a rotational speed of the hydraulic motor to provide an increased rotating torque, a chain drive mechanism 6 composed of a small-diameter sprocket on an input side, a large-diameter sprocket on an output side and an endless chain mounted on the sprockets and adapted to transmit rotation of the speed reduction gear 5 to a drive axle of a below-described drive-axle tire train 7, the drive-axle tire train 7 as rear wheels driven as a result of transmission of rotation of the hydraulic motor 4 via the chain drive mechanism 6, and an idle-axle tire train 8 as front wheels. Incidentally, "HST" is an abbreviation of a hydrostatic transmission which is a type of transmission.
The hydraulic pump 3 is a variable displacement hydraulic pump, which has a bi-directionally tiltable swashplate and can vary a delivery rate of pressure oil. Pressure oil can be delivered in a desired one of normal and reverse directions by operating the swashplate to the corresponding one of positive and negative regions. The rotational speed of the hydraulic motor 4 can be varied in a stepless, continuous manner by changing the delivery rate of pressure oil from the variable displacement hydraulic pump 3. As the hydraulic pump 3 is of the bi-directionally tiltable type, the tired roller can be moved forward or rearward while varying its speed in a stepless manner. In the conventional tired roller, the hydraulic motor 4 is arranged so that the length of its drive shaft extends in a parallel direction, that is, in a direction parallel to the drive-axle tire train 7. The HST (hydrostatic transmission) is constructed by a combination of these variable displacement hydraulic pump 3 and hydraulic motor 4. As a tired roller has a significantly greater vehicle weight than general vehicles, the speed reduction gear 5 is arranged to increase rotating torque to permit traveling of such a heavy tired roller, so that no problem arises concerning travelling of the tired roller. The chain drive mechanism 6 is provided with a bearing 6a, which is disposed upright to rotatably support a rotary shaft of a sprocket of the chain drive mechanism. This upright disposition of the bearing has made it possible to its arrangement in a narrow space between adjacent tires in the drive-axle tire train 7.
Individual tires in the drive-axle tire train 7 and idle-axle tire train 8 are all rubber tires so that, when the tired roller main body 1 is caused to travel, they can rolling-compact and finish a paved surface of asphalt. The drive-axle tire train 7 and the idle-axle tire train 8 are each constructed by mounting many tires, for example, three tires in the case of wide tires or 4 to 5 tires in the case of narrow tires on a drive axle or an idle axle to make up a tire train. In FIG. 10, only the left half of the drive-axle tire train 7 is illustrated, and its right half is not shown. A drive-axle tire train similar to that shown in FIG. 10 is also arranged on the side of the right half. This conventional example is therefore designed in such a way that two tires are mounted on each of the drive axles of the drive-axle tire trains 7 arranged separately on the left and right sides to form a tire train of four tires in total. The tired roller main body 1 is provided with the above-described prime mover 4, hydraulic pump 3, hydraulic motor 4 and speed reduction gear, and also with a fuel tank, a working oil tank and the like. By using remaining spaces where such elements are not arranged, for example, a space above the idle-axle tire train 8 and other spaces, water tanks (not shown) are arranged at various places. These water tanks are formed by surrounding such remaining spaces with walls, and serve to make the vehicle weight greater to provide an increased ground pressure upon rolling compaction. Accordingly, these water tanks account for a substantial part of the volume of the tired roller main body 1, for example, become as heavy as 4 to 5 tons when the total working weight of the tired roller is 15 tons.
For the adoption of the above-described construction, the conventional tired roller is operated as will be described hereinafter. The prime mover 2 is operated to drive hydraulic pump 3. The delivery rate of pressure oil from the hydraulic pump is controlled according to a stroke of an operation lever, whereby the hydraulic motor 4 is driven at a desired rotational speed in accordance with a delivery rate of the hydraulic pump 3. The rotation of the hydraulic motor 4 is then transmitted, in a state increased in rotating torque by the speed reduction gear 5, to the drive axle of the drive-axle tire train 7 via the chain drive mechanism 6, so that the tired roller is allowed to travel at a desired speed without any problem. Further, the traveling direction of the tired roller can be controlled by operating the idle-axle tire train 8 through a steering wheel. Accordingly, the tired roller can travel to and fro on roads and can also travel on paved surfaces for rolling compaction.
In the conventional tired roller, however, the transmission of rotation of the hydraulic motor 4 to the drive-axle tire train 7 requires to transmit rotation of a high torque, which has been obtained by reducing the speed of the first-mentioned rotation at the speed reduction gear 5, through a power transmission. Moreover, for the characteristic feature that a wheel is constructed by the tire train, the power transmission must be arranged in the small space between the adjacent tires in the drive-axle tire train 7. As the power transmission, the chain drive mechanism 6 is therefore used generally. This chain drive mechanism 6 however cannot avoid occurrence of a slack in its chain. Due to this slack, a kick back takes place in the drive-axle tire train 7 upon starting or stopping the tired roller, resulting in the formation of a wave on a road surface finished by rolling compaction. There are hence problems that a great deal of labor is required for manually touching up waves formed by such kick backs and that the finished accuracy of a road surface finished by rolling compaction is insufficient. These problems are worsened especially when rolling-compaction finishing work is performed on a slope or when rolling-compaction finishing work is conducted by employing a tired roller which has been used over a long time. Further, the conventional tired roller requires chain tension adjustments because, for its characteristic feature as a rolling vehicle, the vehicle weight is designed to be significantly heavy compared with general vehicles and its chain becomes longer when used for a certain time. This chain tension adjustment is to apply tension to the chain by cutting the heavy and large chain shorter or by lifting the sprocket, on which the chain is mounted, and changing its mounted position, and is extremely difficult work.